Armature with Spline IK Constraint animation problem
If the track is made from pieces parented to bones:


Select all track pieces
Object > Animation > Bake Action
Check all the boxes and hit OK
Now the animation is baked and should export without problems.


If the track is single piece deformed by Armature modifier:


You will have to bake the animation of bones (same as above but bake to Pose)
Or convert it into Shapekey animation with this script. This will also export fine.